In a broad sense, hybrid vehicles refer to vehicles drive by two or more different types of power sources which are efficiently combined. In general, the hybrid vehicles drive by an engine and an electric motor, and they are called hybrid electric vehicles (HEVs).
In recent years, in order to improve fuel efficiency and develop eco-friendly vehicles, studies on hybrid vehicles are actively ongoing.
Such hybrid vehicles include an engine and an electric motor as power sources. The electric motor is driven by electric power supplied from a battery mounted in the vehicle and includes main components, such as a stator configured to wind a coil around a stator core and a rotor disposed inside the stator, similar to a conventional motor. The rotor includes a permanent magnet into a rotor core.
As such, the electric motor in the hybrid vehicles requires a high-performance permanent magnet in order to obtain high power and high efficiency.
Accordingly, rare-earth permanent magnets having 3 to 5 times stronger magnetic force than ferrite magnets are used in a related art in order to reduce motor weight and improve vehicle efficiency.
However, since such a rare-earth permanent magnet has high conductivity and low specific resistance, eddy currents are generated in the permanent magnet, resulting in an increase in temperature of the permanent magnet. The increase in temperature of the permanent magnet leads to a reduction in magnetic flux density or irreversible demagnetization of the permanent magnet, thereby causing fatal deterioration of motor performance.
In order to resolve these problems, when heavy rare-earth elements resistant to heat are added to a permanent magnet, the manufacturing costs of the permanent magnet may increase, and the amount of rare-earth element preserves is not sufficient compared to other metals.
Accordingly, techniques for decreasing eddy current paths and reducing a loss (iron loss) by manufacturing permanent magnets which are divided axially or laterally have been developed.
However, these techniques increase man-hour since bonding layers are formed on bonding surfaces of the permanent magnets and deteriorate productivity since post-treatment processes such as surface grinding for adjusting flatness and surface coating for improving corrosion resistance are required after bonding the permanent magnets.
In addition, the permanent magnets may be broken at their corners during the surface grinding thereof, thus deteriorating production qualities of the permanent magnets.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.